“They said, ‘Well, we need a physical barrier in certain places, we need technology across the board, and we need more people,'” he said.

“The president still says ‘wall’ – oftentimes frankly he’ll say ‘barrier’ or ‘fencing,’ now he’s tended toward steel slats. But we left a solid concrete wall early on in the administration, when we asked people what they needed and where they needed it.”

What has Mr Trump said?

“I would build a great wall, and nobody builds walls better than me, believe me, and I’ll build them very inexpensively, I will build a great, great wall on our southern border. And I will have Mexico pay for that wall.”

These were the words Mr Trump spoke on 16 June 2015 as he launched his presidential campaign. At the same time, he called Mexican “rapists” and drug dealers were entering the US.

In the early months of his campaign, he attacked rival Jeb Bush for calling his proposal a “fence”.

In January, Mr Trump said the idea had not changed since its conception and that it was still very much a wall, with one caveat.

His tone has changed since then, although only in the past year.

When visiting prototypes for the wall in March (that included large concrete options) he said “you have to have see-through…you have to know what’s on the other side of the wall”.